A. Field of the Invention
The present invention relates generally to a drill string sub having a side entry port for insertion and removal of wireline cable and more particularly to a side entry sub with a tension release wireline cable clamp.
B. Description of the Prior Art
The drilling and completion of oil or gas wells commonly involves the use of apparatus made up of a drill string having a steering tool or a plurality of logging tools positioned within or affixed to the drill string near its lower end. A communication wireline cable is often used for transmitting to the surface the information gathered by such tools.
Devices known as "mud motors" or "turbo drills" are often employed during well drilling operations. These devices are attached at the lower end of the drill string above the bit. During mud motor drilling operations, high pressure drilling mud is circulated down the interior of the drill string, through the mud motor and bit and up the annulus of the well bore. The action of the mud in the mud motor rotates the bit without rotating the drill string. Mud motor drilling is particularly useful in the drilling of deviated holes where the bit may be kicked out by the use of a bent sub. During such mud motor drilling operations, a steering tool is often positioned inside the drill string above the mud motor. The steering tool monitors the inclination and azimuth of the well bore during drilling, so that course corrections may be continuously made.
Additionally, there has recently been developed a system for logging a zone of interest by the use of drill pipe. Conventional open hole wireline logging of highly deviated or bad holes is often impossible because logging tools cannot be lowered into the zone of interest by gravity. Pump-down techniques, often used in highly deviated holes, are both time consuming and expensive.
One method for establishing communication with steering or down hole logging tools in drill pipes involves insertion of a wireline cable through a port in an element of the drill string known as a "side entry sub" to form a hard wire link between the down hole tool and the surface. Thus, a fixed length of cable is contained within the drill string below the side entry sub. The cable between the side entry sub and the surface extends outside the drill string.
One benefit of the wireline cable's entry through a side entry sub stems from the fact that new drill pipe sections may be added to the drill string without first withdrawing the cable from the well bore. In contrast, if the wireline cable is run totally inside the drill string from the surface to the down hole tool, the most feasible method for adding a pipe section to the drill string involves the complete removal of the cable from the drill string, followed by addition of the new pipe section, and reinstallation of the cable. Inclusion of a side entry sub in the drill string renders unnecessary such repeated cable reinstallation, increasing the speed of operation, and lowering its cost.
Typically, in the case of logging, the bottom hole tools are assembled and then lowered into the hole on drill pipe to a depth directly above the interval of open hole to be logged. The logging cable is passed through the port of the side entry sub and connected with an electrical connector or latch. The sub is then made up to the drill string and the latch and cable are lowered or pumped down inside the drill string to the logging assembly. Once the logging cable is latched to the logging assembly, the cable is clamped mechanically to the side entry sub, whereupon additional lengths of drill pipe may be made up and lowered into the hole.
When the cable is in place, it is possible to circulate through the drill string and reciprocate the drill string. However, it may be desired to remove the cable from the drill string during drilling or logging operations, for example, if the cable becomes damaged. Another important reason for removing the cable would be to vacate the drill pipe after it has become stuck. Retaining a length of cable inside such drill pipe would severly hamper the running of tools, such as free-point indicators and explosive devices, down the interior of the drill string. Also, if the drill string must be rotated, the portion of cable extending along the outside of the drill string and running to the surface would probably be damaged and would severly interfere with drill string rotation. When it is desirable to remove the cable from the drill string, the cable usually is removed by retrieving it through the port in the side entry sub.
The presently existing side entry sub cable clamp includes a pair of clamp parts that are fastened about the cable by bolts or the like. The fastened together clamp parts are in turn connected by shear pins to the side entry sub. When it is desired to retrieve the cable, a tension force is exerted on the cable sufficient to shear the shear pins and the cable and sheared clamp parts are pulled to the surface. When the clamp parts reach the surface, they are removed from the cable and the cable is then pulled the rest of the way out of the hole.
The removal of the clamp parts is a time consuming operation. The reeling up of the cable must be slowed down when it is expected that the clamp parts will reach the surface and must be stopped entirely when the clamp parts are removed. Since the pulling of the cable is normally pursuant to some emergency, time is of the essence.
Accordingly, it is an object of the present invention to provide a side entry sub with a tension releasable cable clamp that does not have to be removed from the cable as the cable is pulled from the hole. It is a further object of the present invention to provide a side entry sub with a tension releasable cable clamp wherein the cable clamp remains with the side entry sub after the cable is released.